Lithium polymer batteries comprise electrode assemblies comprising separators positioned between positive and negative electrode plates. The separator acts as a medium for ion conduction, similar to an electrolyte. The separator also performs separation in the lithium ion battery. These separators generally comprises gel-type polymer electrolytes formed by impregnating polymers with an electrolyte for improved ion conductivity.
Lithium polymer batteries are generally encased in thin pouches and sealed to reduce the risk of leakage of the gel-type electrolyte. The pouch comprises a thin metallic foil having two surfaces, one surface coated with cast polypropylene, and the other surface coated with vinyl.
Lithium polymer batteries generally have protective circuit modules fastened to predetermined regions of the pouches. The protective circuit modules protect the batteries from voltages and currents generated during overcharge, over-discharge, short circuits, and the like. The protective circuit modules are typically connected to the electrode assemblies by positive and negative electrode tabs which extend a predetermined length from the exterior of the pouch. Various semiconductor devices and passive devices are mounted on the protective circuit modules to sense voltages and currents during overcharge, over-discharge, short circuits, and the like. These devices include comparative circuits, logic circuits, and field effect transistors for charge/discharge switches.
When external apparatuses such as laptop computers and PDAs are equipped with these conventional lithium polymer batteries, the protective circuit module may be directly short-circuited to the peripheral circuit of the external apparatus. More particularly, the wiring pattern of the semiconductor devices mounted on the protective circuit module may be short-circuited to the peripheral circuit of the external apparatus. Such short circuits cause battery malfunction and may damage the external apparatus.
The electrode tabs of conventional lithium polymer batteries are generally “U” or “Z” shaped. The electrode tabs are electrically connected to the protective circuit module to suppress any increase in battery thickness caused by the protective circuit module. More specifically, the protective circuit module is positioned on an additional pouch in front of the electrode assembly. The electrode tabs are bent several times to achieve a “U” or “Z” shape, and are connected to the protective circuit module. Accordingly, conventional lithium polymer batteries require numerous processing steps for mounting the protective circuit module and comprise complicated exteriors. These conventional lithium polymer batteries are also quite long because the protective circuit module is positioned in front of the electrode assembly pouch.